The present invention relates generally to methods and apparatuses for processing microfeature workpiece samples.
During the development and production of microfeature workpieces, such as wafers, engineers periodically conduct destructive tests of selected workpieces to evaluate the efficacy of new and/or existing processes. One technique for carrying out such tests includes cutting a sample section from the microelectronic wafer, then grinding the sample to expose a feature of interest. The feature of interest is then examined with a transmission electron microscope (TEM). If necessary, the processes performed on subsequent wafers can be adjusted to correct any defects identified during the TEM examination.
FIG. 1 is partially schematic illustration of an apparatus 10 for performing the foregoing process. Such an apparatus is available from South Bay Technology of San Clemente, Calif. The apparatus 10 includes a body 11 into which two micrometer legs 20a, 20b are threadably inserted. The apparatus 10 can optionally include a third micrometer leg 20c. A sample holder 30 is fixedly attached to the body 11 and supports a sample 40, which is cut from a wafer. The apparatus 10 is then positioned adjacent to a grinding surface 51 of a grinding wheel 50. While the grinding wheel 50 rotates (as indicated by arrow R), an edge 39 of the sample 40 protruding from the sample holder 30 contacts the grinding surface 51, as do contact surfaces 21 of the micrometer legs 20a, 20b. Accordingly, the micrometer legs 20a, 20b can support the sample 40 in a fixed orientation relative to the grinding surface 51 while the sample 40 is ground down to expose the feature of interest.
FIG. 2 illustrates details of a sample 40 configured in accordance with the prior art. The sample 40 can have a plurality of active areas 43, each of which includes features of interest. Typical features of interest include container-shaped capacitors 44 that are electrically coupled to contacts 45 and are separated from an intermediate contact 47 by gate runners 46. It is typically desirable to grind the sample 40 down to a cleavage plane 48 to expose adjacent features within at least one of the active areas 43. Because the cleavage plane 48 is generally parallel to significant, readily visible features of the sample 40 (such as an array edge 41 or a metal runner 42), and because these features are typically aligned with a crystal plane of the wafer from which the sample 40 is extracted (as indicated by parallel axis X), it is relatively straightforward to precisely grind the sample 40 down to the cleavage plane 48 and expose the features of interest for TEM examination. For example, the sample 40 can be cut from its wafer by eye (i.e., without using a precise, machine-guided alignment process) so that the edge 39 of the sample 40 is at least approximately parallel to the cleavage plane 48. The operator can then iteratively: (a) adjust one of the micrometer legs 20a or 20b (FIG. 1) relative to the other; (b) grind the sample 40; and then (c) examine the edge of the sample 40 with reference to the array edge 41, the metal runner 42, or another easily visible feature parallel to the cleavage plane 48. Accordingly, the operator can orient the edge 39 of the sample 40 to be parallel with the cleavage plane 48. Once this orientation is obtained, the sample 40 can be ground down, as discussed above, until the features of interest at the cleavage plane 48 are exposed.
As the semiconductor industry moves to fit more active areas 43 into each wafer, some wafers have active areas 43 oriented such that the desired cleavage plane 48 exposed during destructive testing is no longer aligned with either the crystal plane (e.g., the X axis) or the easily visible features (e.g., the array edge 41 and/or the metal runner 42) of the sample 40. As a result, the initial cut that forms the edge 39 of the sample 40 is made at a significant angle relative to the X direction and the easily visible features. This operation can produce an initial cut that is misaligned by several degrees relative to the desired cleavage plane 48. Such a large misalignment is not easily corrected by the iterative method described above. For example, if the micrometer legs 20a, 20b, are adjusted to have significantly different lengths (to account for the initially misaligned cut), the corresponding contact surfaces 21 become highly faceted rather than flat (as indicated in an exaggerated fashion by phantom lines in FIG. 1). When the faceted micrometer legs 20a, 20b are subsequently rotated for further adjustment, the relative offset between the legs becomes unpredictable because the contact surfaces 21 are faceted rather than flat. This in turn can cause the sample 40 to be misoriented. If the sample 40 is not properly oriented, the desired features of interest will not be exposed during grinding, defeating the purpose for forming the sample.